The present invention relates to an equipment cabinet for electronic and electrical insertable units that includes a self-supporting rack for holding the insertable units as well as metal casing components including side walls, a rear wall, a door, a top and a bottom.
Equipment cabinets for accommodating electronic components must meet a number of requirements. For example, these cabinets must have excellent mechanical strength--also with respect to vibratory stresses and during earthquakes. The additionally required good accessibility for the inserted units requires easily removable casing components which not only provide protection against dust and water but also against electromagnetic radiation.
In order to realize optimum high frequency shielding, it has been attempted in the past to use the casing to form the most gap-free, closed, electrically conductive casing around the equipment cabinet. This has been done by producing a plurality of conductive connections between the various casing components and the rack and between the rack components themselves as well as between the individual casing components. These procedures required careful, expensive manual labor in the assembly of the equipment cabinet and particularly a very good, electrically conductive, supporting rack as it can be realized by way of electroplating surface refinement, for example with nickel, or by the use of stainless steel. It is not possible to selectively or subsequently provide an HF shield for racks that were manufactured for simple applications in an inexpensive manner and without consideration of shielding measures.
Another solution of the shielding problem is the insertion of the rack in a box that is closed on all sides, is soldered or welded shut and on which rests a door that is provided with contacts; however, the drawback here is the poor accessibility of the inserted components since access is possible only through the opened door.
An equipment cabinet gasket is known which includes a frame-type rack to which the casing components, namely walls, door, top and bottom are fastened. The frame rack is composed of metal profiles that are provided with outwardly projecting flanges or strips onto which sealing strips are clamped. These sealing strips are made of rubber and, for fastening purposes, are provided with a spring-elastic insert that has a U-shaped profile and is provided with barbs. On its exterior, the sealing strip is covered with a conductive braided metal structure that electrically connects the frame rack with the screwed-on casing components. The metal profiles and the sealing strip are of an expensive design, a gap-free HF shield is hardly realizable (unexamined published European Patent Application EP 0,427,550).
Also known is a switch cabinet including a frame rack that is provided with an all-around casing equipped with a door. A box-shaped insert that is closed on all sides and is pushed into the frame rack serves as the HF shield. A shielding plate is inserted into the interior face of the door. For the purpose of sealing, the edges of the insert as well as those of the shielding plate are provided with plug-in, resilient contact strips which, when the door is in the closed position, are congruent with one another. However, the desired high frequency shield is here obtained at high expense in the form of an insert (German Patent 3,611,693 which corresponds to U.S. Pat. No. 4,760,496).
Sealing strips for sealing and shielding slits and crevices in devices to be shielded where the sealing strips are composed of a cord of braided metal and a vulcanized-on rubber sealing profile are disclosed in Unexamined Published German Patent Application DE 2,829,255.